1. Field of the Invention
The present invention relates to an aluminum alloy casting having a high strength and a high toughness (hereinafter simply referred to as an "aluminum alloy casting") which is appropriate for parts, such as automotive parts or the like, which are required to have a strength and a toughness, and to a process for producing the same.
2. Description of the Related Art
There has been an aluminum alloy forged product, for instance, "6061" or the like as per Japanese Industrial Standard (hereinafter abbreviated to as "JIS"). It has been known that it provides the following advantages. Namely, it has less internal defects, it is superior in the strength and toughness, and accordingly it is highly reliable in view of quality. However, it suffers from a high cost.
On the other hand, an aluminum alloy casting, for instance, a casting made from "AC4C" or the like as per JIS, provides an advantage because it is less expensive than the aluminum forged product. However, completed parts should be enlarged because the aluminum alloy casting has a lower strength and a lower toughness, and because it is less reliable. Accordingly, the parts suffer from increased weights, and the merits of the weight reduction resulting from the aluminum alloy casting application have been diminished.
Silicon (Si) which has been added to improve the castability of the aluminum alloy is believed to be one of the causes which deteriorates the strength and the toughness of an aluminum alloy casting. In particular, Si is believed to deteriorate the toughness.